The present invention relates generally to an exposure apparatus for exposing a plate as an object, and more particularly to cooling of the object in the exposure apparatus that uses light in the X-ray and ultraviolet regions or electron beams as exposure light.
In exposure, an exposure apparatus irradiates exposure light onto a wafer and causes wafer's thermal expansions. A wafer chuck usually restrains the wafer, and thus an offset between them seldom occurs.
However, when the shearing force exceeds the chuck's restraint force, the wafer offsets from the wafer chuck. Cooling of the wafer is necessary to avoid the offset and to reduce the wafer's expansion.
Conventional exposure apparatuses use an i-line lamp having a wavelength of about 365 nm, a KrF excimer laser having a wavelength of about 248 nm, and an ArF excimer laser having a wavelength of about 193 nm as a light source, and the light from the light sources with these wavelengths does not attenuate in the air and is applicable to exposure in the air.
The exposure in the air enables the gas to be filled between the wafer and the chuck, the energy applied to the wafer to be transmitted to the chuck through the gas between them, and the heat to be collected by cooling the wafer held by the chuck with coolant. Cooling using heat transmissions through the air from a wafer surface is available. See, for example, Japanese Patent Application No. 09-306834, corresponding to U.S. Pat. No. 6,084,938.
It is predicted the advanced fine processing of the recently promoted semiconductor integrated circuits advances will use a shorter wavelength of the exposure light down to the extremely ultraviolet light having a wave range between 5 and 20 nm.
However, the EUV light attenuates greatly in the air and is viable only in the vacuum environment in which cooling using the heat transmissions through the air is not available. The temperature control becomes thus difficult in the vacuum environment.
The electron beam also greatly attenuates its energy in the air, and faces similar difficulties when is used as the exposure light.
Most conventional cooling methods in the vacuum are classified into a cooling method that uses heat conductions in the solid through coolant, and a method for controlling the temperature of a target by directly controlling the temperature of a radiation plate.
The heat flux in the radiation heat transfer is very small between two objects with a small temperature difference between them. Efficient heat transfer needs a large heat flux, and therefore a large temperature difference between the wafer and the radiation plate is needed for efficient heat transfer. This condition requires the significantly lowered temperature of the radiation plate. On the other hand, it is difficult for such a temperature control means that directly controls the radiation plate using a Peltier element, etc. to suddenly change the radiation plate's temperature. When the thermal load turns on and off, as the exposure heat, the temperature control means cannot follow the temperature changes of the object to be controlled.
In addition, a so-called scanner for scanning a reticle and a wafer relative to the exposure light, and for exposing a reticle pattern onto the wafer generally fixes an exposure position and moves a stage relative to the exposure position for exposure. Thus, as the stage moves, an exposed and heated area moves on the wafer. Therefore, fixing of a cooling position causes a distortion in the wafer when the stage's moving direction changes because unheated part is cooled.
Responsive radiation cooling and switching of a cooling position have been thus demanded.